The present invention relates to barium ferrite particles of magnetic properties, especially not more than 1,000 Oe of a coercive force suitable for use as a magnetic material for magnetic recording. And the present invention relates to a process for producing the barium ferrite particles.
Hitherto, the barium ferrite particles have been obtained by igniting a mixture of iron(III) oxide and barium carbonate at high temperature in the air, and the thus-produced particles have more than 3,000 Oe of the coercive force. Therefore, such a barium ferrite particles are not suitable for use as the magnetic material for magnetic recording and in fact they are widely used as a permanent magnet.
Another method for producing the barium ferrite particles comprises subjecting an alkaline suspension containing ferric ions and barium ions to autoclaving. In this method, a ferromagnetic precipitate, barium ferrite, consisting of hexagonal plate-like particles, can be obtained and at the same time nonferromagnetic precipitates, .alpha.-Fe.sub.2 O.sub.3, are also formed depending on the reaction conditions. In addition, the magnetic properties of the ferromagnetic particles obtained also widely vary since a variety of the particles in particle size are produced depending on the reaction conditions. Therefore, the barium ferrite particles having the magnetic properties suitable for use as the magnetic material for magnetic recording can be hardly obtained by this method.
An object of the present invention is to improve the latter method so as to obtain the barium ferrite particles having the magnetic properties suitable for use as the magnetic material for magnetic recording.
This and other objects of the present invention will be apparent from the following descriptions.
The foregoing and other objects of the present invention will be accomplished by the process of the present invention, wherein the prior art is improved based on the finding that a specific surface area of the barium ferrite particles should be not more than 5 m.sup.2 /g to obtain the particles having the coercive force of not more than 1,000 Oe.
The terminology used herein is defined as follows:
"Specific surface area" is intended to refer to the value measured by the BET method. PA0 "Coercive force" is intended to refer to the value measured at a degree of packing density of 1.6 g/cm.sup.3. PA0 "Maximum magnetization" is intended to refer to the value measured by the VSM method at the magnetic field of 10 kOe. PA0 "Apparent density" and "tap density" are intended to refer to the values measured following JIS K 5101.